1. Field of the Invention
This invention relates to a gate array, and, particularly, to a Bi-CMOS gate array comprising bipolar transistors and CMOS ( Complementary Metal Oxide Silicon transistors arranged in the form of an array.
2. Description of the Prior Art
Semiconductor integrated circuits ( ICs ) are indispensable for miniaturization and a reduction in power consumption of various electronic devices and appliances. Custom ICs tend to be expensive because its volume of manufacture is relatively small and it takes a relatively long period of time for development, and, thus, it has often been the case to use discrete components and standard ICs in combination to construct desired circuits. In order to satisfy the demand for inexpensive custom ICs, a gate array has been developed. In the case of a gate array, the manufacturer has already prepared the so-called master chips, on which unit cells comprised of standardized resistor and transistor elements are arranged regularly and the diffusion process of which has already been completed. The manufacturer then produces an interconnection mask in accordance with the circuit design which meets the user's specification, and, then, using such a mask, an interconnection pattern of Al or the like is formed on the master chip, thereby completing the wafer processing. In this manner, in the case of a gate array, using different interconnection patterns, various ICs having different circuit configurations may be obtained from the master chips of identical structure. Since it is only necessary to design an interconnection pattern, only a short period of time is required to provide an IC chip having a desired function.
Heretofore, gate arrays have been formed either from bipolar transistors or from MOS transistors exclusively. However, in some applications, it is often required to use not only the characteristics of bipolar transistors but also the characteristics of MOS transistors, and, in such circumstances, it is obliged to use a plurality of IC chips in order to attain a desired function, which is apparently disadvantageous.